CVE-2024-26618 in Linux
Summary
by MITRE • 03/11/2024
In the Linux kernel, the following vulnerability has been resolved:
arm64/sme: Always exit sme_alloc() early with existing storage
When sme_alloc() is called with existing storage and we are not flushing we will always allocate new storage, both leaking the existing storage and corrupting the state. Fix this by separating the checks for flushing and for existing storage as we do for SVE.
Callers that reallocate (eg, due to changing the vector length) should call sme_free() themselves.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 02/15/2025
The vulnerability identified as CVE-2024-26618 resides within the Linux kernel's arm64 subsystem, specifically affecting the Scalable Matrix Extension (SME) implementation. This issue manifests in the sme_alloc() function which handles memory allocation for SME storage contexts. The flaw represents a critical memory management error that can lead to resource leakage and system instability. The vulnerability impacts systems utilizing arm64 architecture with SME support, particularly those running kernel versions where this specific code path has not been patched. The issue is classified under CWE-401 as a failure to release memory resources, and it aligns with ATT&CK technique T1070.004 for indicator removal through deletion of system logs, though in this case the deletion manifests as improper memory handling rather than log deletion.
The technical root cause of this vulnerability stems from improper conditional logic within the sme_alloc() function. When the function is invoked with existing storage parameters and the system is not performing a flush operation, the current implementation fails to properly distinguish between the flushing requirement and the existing storage condition. This logical flaw causes the function to always allocate new storage regardless of whether existing storage is already available, resulting in a memory leak where the previously allocated storage becomes unreferenced and inaccessible. The function's behavior violates proper resource management principles by not correctly handling the state transition between existing and new storage allocation. The fix implements a separation of concerns between the flushing check and existing storage check, mirroring the established pattern used for SVE (Scalable Vector Extension) implementations which already handle these conditions correctly. This approach ensures that when existing storage is present and no flushing is required, the function properly utilizes the existing resources rather than creating redundant allocations.
The operational impact of this vulnerability extends beyond simple memory leakage to potentially compromise system stability and performance. Memory leaks in kernel space can accumulate over time, leading to progressive system degradation and eventual resource exhaustion. When multiple allocations occur without proper cleanup, the system may experience increased memory pressure and reduced overall performance. In high-frequency allocation scenarios, this can result in system instability or even complete system crashes. The vulnerability particularly affects systems with frequent SME context switching or vector length changes, where the allocation and deallocation cycles are more frequent. The improper state management can also lead to unpredictable behavior in applications that rely on SME for high-performance computing tasks, potentially causing data corruption or application failures. This vulnerability is especially concerning in server environments where sustained operation and resource efficiency are critical for maintaining service availability and performance.
Mitigation strategies for CVE-2024-26618 require immediate kernel updates to address the core memory management flaw. System administrators should prioritize applying the patched kernel version that implements the corrected conditional logic in sme_alloc(). For environments where immediate patching is not feasible, monitoring for memory usage patterns can help detect potential leakage symptoms, though this represents only a workaround rather than a permanent solution. The fix requires careful attention to caller behavior, as functions that need to reallocate storage due to vector length changes must properly invoke sme_free() before calling sme_alloc() again. This change in calling convention ensures that existing storage is properly released before new allocation occurs, preventing the accumulation of leaked resources. Organizations should also implement comprehensive testing procedures to validate that SME-related applications behave correctly after the patch is applied, particularly focusing on memory usage patterns and context switching behavior. The recommended approach aligns with industry best practices for kernel security updates and follows the principle of least privilege by ensuring proper resource management at the kernel level.